Re: gEDA-user: pcb crooked traces

[Steven Michalske <smichalske@xxxxxxxxx>]

> The user has a connector with metric spaced pins.  When the metric value is
> input, the value is rounded off to the nearest 0.01 mil giving an error of
> 0.005 mil.  At this point there is no way to recover that error, it is
> recorded in the system that way and the precision is lost.  This value is
> used to calculate the position of all the pins in the connector resulting in
> an accumulated error of 0.005 * N.  At 100 pins this the accumulated error
> is 0.5 mil.  That may not be a show stopper, but I would prefer to avoid it
> if possible.  At 200 pins the accumulated error is 1.0 mil, etc.  Clearly
> this is quickly reaching a point of being very unacceptable.


This example is not what we do in PCB,  we do not itterate the pin positions.

The only place this error would occur is in generating the footprints,
not in pcb.

It's wrong

When you do these operations you perform all math in the defined
units, mil, mm, parsecs, or whatever.
Then you do one conversion to the target unit.

If floating point numbers wer the end all solution why do banks still
use BCD math?  Because it removes the errors you are talking about.
But we wouldn't use BCD math it's not required.

Yes it seems that we will be using nanometer units as the base unit.
See the email from DJ, It has his seal of approval, and chances are
thats what will be implemented.

Steve


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